1. Field of the Invention
The present invention relates to assembling distributor sectors, bearing fixed blades, and ensuring correction of a gas flow in a casing enclosing stators of a turbomachine.
2. Description of the Related Art
The external flow of gases in turbomachines is delimited by distributor and ferrule sectors alternately mounted on the casing via overlapping hooks along the machine. With reference to FIG. 1, which illustrates an already known assembly, a straightening sector 1 bears a pair of assembly flanges 2 and 3, respectively at the front and at the rear, and which are both fitted with end hooks 4 and 5, extending in the longitudinal direction of the machine. The end hook 4 at the front is placed on a hook 6 of a casing 7 by a pair of mutual support faces 8, which hold the sectors 1 against centripetal radial movements in the machine; the end hook 5 of the other flange 3 abuts radially towards the outside against the casing 7 by a pair of faces 9, and towards the rear, against a second hook 10 of the casing 7, by a pair of flat stop faces 11. A clip 12 is placed around the second hook 10 below the second end hook 5 to also guard the sectors 1 against centripetal movements. The sectors 7 comprise more projections 13 towards the front, which encircle the rear of ferrule segments 14 between them and the first hooks.
This assembly holds the sectors 1 against the movements produced by the radial and axial forces oriented towards the rear during operation. Assembling these conventional devices is difficult to carry out, as the inclined sectors 1 have to be disposed in the casing 7 so that the rear flange 3 can be inserted in the second hook 10 before making them pivot about the end hook 4 at the front, so that the end hook 5 can be inserted behind the hooks 10 with a radial movement towards the outside. In order to effect this assembly, it is necessary to have two major sets of rotor-stator in the internal stream, with such a requirement being detrimental to the seals between rotor and stator. Finally, probably the most serious disadvantage of this assembly is the fact that the hooks 6 and 10 are integrally formed with the casing 7, being subjected to significant mechanical and thermal stresses since they are near the stream of hot gases. As such, it becomes necessary to construct the hooks 6 and 10 and the casing 7 from a sufficiently resistant material even though the casing 7 is subjected to a lower temperature. In addition, due to the integral construction, fatigue cracking can appear in the hooks 6 and 10 and spread to the point where the entire casing 7 needs to be replaced.
Therefore, a need exists to rectify the design of the above-described casing, which is both costly and fragile, while enabling straightening sectors to be mounted more simply and producing a more rigid and less complex assembly. The instant invention satisfies these various requirements.